Converter socket terminal

ABSTRACT

A socket terminal assembly includes a socket body having an end with an opening and an opposite end configured to contact the corresponding connection region of a printed circuit board, a contact spring, disposed at the opening of the socket body, to receive and apply a frictional force sufficient to retain the lower end of a pin within the opening of the socket body; and a resilient member, disposed within a lower end of the opening, to apply, to the pin and in response to a downward force applied to the pin, an upward force sufficient to overcome the frictional force of the contact spring. The pin has an end adapted to contact an electrical contacting area of an integrated circuit package and an opposite end configured to be inserted within the opening of the socket body. An intercoupling component includes a socket support member having holes, each hole receiving a corresponding socket terminal assembly.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT/US98/23358, filed Nov. 2, 1998, which is a continuation of U.S. Application Ser. No. 08/963,277, filedNov. 3, 1997 now U.S. Pat. No. 5,877,554.

BACKGROUND OF THE INVENTION

This invention relates to making connections between integrated circuitarray packages (IC) and circuit boards.

Ball grid array (BGA) and land grid array (LGA) packages are becomingincreasingly popular because of their low profiles and high densities.With a BGA package, for example, the rounded solder balls of the BGA aregenerally soldered directly to corresponding surface mount pads of aprinted circuit board rather than to plated thru-holes which receivepins from, for example, a pin grid array IC package.

Sockets are used to allow particular IC packages to be interchangedwithout permanent connection to a circuit board. More recently, socketsfor use with BGA and LGA packages have been developed to allow thesepackages to be non-permanently connected (e.g., for testing) to acircuit board. However, problems can exist in attaching a BGA package toconventional sockets. This is because a BGA package presents anon-traditional mating condition. The rounded solder balls of the BGAare themselves relatively poor points of contact for socketing, suitedonly for their intended purpose of being reflowed. Further, theco-planarity between the individual points of contact for each roundedsolder ball may be lacking due to ball irregularities and warping of theBGA package.

SUMMARY OF THE INVENTION

This invention features a socket terminal assembly which provides areliable, non-permanent and low-loss electrical interconnection betweenelectrical contacting areas of an array package and connection regionsof a substrate (e.g., printed circuit board) while duplicating themating condition normally present between the electrical contactingareas and connection regions. The term “integrated circuit arraypackage” is intended to mean those packages, including PGA (pin gridarray), BGA and LGA packages. The term “substrate” is intended to meanany base member having electrical contact areas including printedcircuit boards, IC chip substrates or the packages supporting such chipsubstrates.

In one aspect of the invention, the socket terminal assembly includes acontact spring, disposed within an opening of a socket body, to receiveand apply a frictional force sufficient to retain a pin within theopening of the socket body; and a resilient member, disposed within theopening, to apply, in response to a downward force applied to the pin,an upward force to the pin sufficient to overcome the frictional forceof the contact spring. The pin is adapted to contact the electricalcontacting area of the integrated circuit array package. The socket bodyhas an end configured to contact the corresponding connection region ofthe substrate and an opposite end having the opening for receiving thelower end of the pin.

Preferred embodiments of this aspect of the invention may include one ormore of the following features. The contact spring is configured toprovide a “wiping”, reliable electrical contact in which the frictionalforce sufficient to retain the pin within the socket body is in adirection substantially transverse to the upward force applied by theresilient member. For example, the contact spring includes resilientspring fingers which frictionally engage the lower end of the pin. Theresilient member for applying the upward force, on the other hand, is inthe form of a coiled conductive spring, or alternatively, in the form ofan elastomeric material (e.g., rubber).

The lower end of the socket body is ball-shaped or may include a solderball attached thereto. The upper end of the pin includes aball-contacting surface which is concave to receive a ball-shapedcontact of a ball grid array package. A sharp protuberance extendingfrom the ball-contacting surface may be provided to pierce the surfaceof the ball-shaped contact. The sharp protuberance is conically-shapedand disposed along the longitudinal axis of the pin. In otherembodiments, the sharp protuberance may be ring-shaped and disposedconcentric with the longitudinal axis. Alternatively, the upper end ofthe pin includes particle interconnections.

In another aspect of the invention, an intercoupling component (e.g., asocket assembly) includes a number of socket terminal assemblies, of thetype described above, all of which are positioned within an array ofholes or apertures in an insulative support member and configured toelectrically connect the electrical contacting areas of the integratedcircuit array package with the array of connection regions of thesubstrate. The array of holes in the support member are located in apattern corresponding to the array of electrical connection regions ofthe substrate.

An intercoupling component having this arrangement eliminates the needfor soldering the package directly to a circuit board (e.g.,motherboard) and allows removing the integrated circuit array package insituations where the package needs to be repaired or replaced.

Preferred embodiments of this aspect of the invention may include one ormore of the following features. The intercoupling component furtherincludes an electrically insulative sheet coupled to the pins and havingholes arranged in a pattern of the connection contacts. The sheet isformed, for example, of a polyimide film and adapted to retain the pinsin a ganged arrangement. The intercoupling component further includes amember which applies a downward force on the contact area of theintegrated circuit package and to each pin to cause the resilient memberto compress. The member is a heat sink threadingly received within acover positioned over the integrated circuit package. The terminalsupport member includes alignment elements to align the contacting areaof the integrated circuit package to corresponding ones of theconnection regions.

In another aspect of the invention, an intercoupling component includesa retaining member coupled to a plurality of pins received within acorresponding plurality of sockets which, in turn, are received within asocket support member having a detent. The returning member isconfigured to cooperate with the detent so that each of the pins aremaintained with the sockets.

Preferred embodiments of this aspect of the invention may include one ormore of the following features. The retaining member includes arelatively thin, electrically insulative, flexible sheet member (e.g.,formed of polyimide) having holes extending therethrough and arranged ina planar configuration about the sheet to correspond with thepredetermined positioning of the pins in the sockets. Each of the pinsincludes a head at the upper end of the pin, the head having an inwardlyextending groove along its periphery. Each hole of the flexible sheethas a peripheral edge extending into a corresponding groove of the headof the pin. The detent is an opening formed in a sidewall which extendsvertically from the upper surface of the socket support member andreceives an edge of the flexible sheet. A detent may be formed in eachof a pair of opposing sidewalls of the socket support member.

In another aspect of the invention, a terminal for electrically connecta solder ball contact area of a ball grid array package to acorresponding connection region of a substrate includes a head having aball-contacting surface with a sharp protuberance extending verticallyfrom a lowest point of the ball-contacting surface and below a highestpoint of the ball-contacting surface. The ball-contacting surface isconcave and conically-shaped to receive the solder ball contact area.The sharp protuberance is configured to pierce the surface of the solderball.

In embodiments of this aspect of the invention, the sharp protuberanceis conically-shaped and lies along the longitudinal axis of theterminal. Alternatively, the sharp protuberance may be ring-shaped anddisposed concentric with the longitudinal axis.

Other features of the invention will be apparent from the followingdescription of the preferred embodiments and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded, somewhat diagrammatic, isometric view of a BGAconverter socket assembly, a BGA package, and hold-down assemblypositioned over a printed circuit board.

FIG. 2 is a cross-sectional side view of a portion of the BGA convertersocket assembly of FIG. 1.

FIG. 3 is a perspective view of a contact spring of the BGA convertersocket of FIG. 2.

FIG. 4 is a perspective view of the head region of a pin which receivesthe solder balls of the BGA package of FIG. 1.

FIG. 4A is a cross-sectional side view of an alternative embodiment ofthe head region of a pin.

FIGS. 5A-5B are cross-sectional side views of the operation of the BGAconverter socket assembly.

FIG. 6 is a cross-sectional side view of a second embodiment of a BGAconverter socket assembly.

FIG. 7 is a perspective view of an alternative embodiment of the contactspring of the BGA converter socket assembly of FIG. 6.

FIG. 8 is a cross-sectional side view of a third embodiment of a BGAconverter socket assembly.

FIG. 9 is a cross-sectional side view of a fourth embodiment of a BGAconverter socket assembly.

FIG. 9A is a perspective view of the contact spring of the BGA convertersocket assembly of FIG. 9.

FIG. 10 is a cross-sectional side view of a fifth embodiment of a BGAconverter socket assembly.

FIG. 11 is a cross-sectional side view of a sixth embodiment of a BGAconverter socket assembly.

DESCRIPTION

Referring to FIGS. 1 and 2, a BGA socket converter assembly 10 forintercoupling a BGA package 12 to a printed circuit board 14 is shown.BGA socket converter assembly 10, serving as an intercoupling component,includes an electrically insulative member 16 for supporting convertersocket terminals 18, each of which is press-fit within a correspondingone of an array of holes 20 (FIG. 2) in the insulative member. The arrayof holes 20 are provided in a pattern corresponding to a footprint ofrounded solder balls 22 (FIG. 5B) of BGA package 12 as well as afootprint of surface mount pads 24 of printed circuit board 14.Insulative member 16 with converter socket terminals 18 is press-fitinto a guide box 26 having sidewalls 28 along which the peripheral edgesof BGA package 12 are guided so that solder balls 22 are aligned overconverter socket terminals 18. Insulative member 16 and guide box 26 maybe formed as a one-piece, integral unit, shown for example in FIG. 6.

BGA socket converter assembly 10 also includes a hold-down cover 30 forsecuring the BGA package 12 into the socket converter assembly. Cover 30includes a pair of opposite walls 31 having tab members 33 which engagerecessed portions 37 along the underside of insulative member 16.Hold-down cover 30 includes a threaded thru-hole 34 which threadinglyreceives a heat sink 32 to provide a thermal path for dissipating heatfrom the IC device generated within BGA package 12. Heat sink 32 isinserted and backed-in from the bottom of the cover 30 and includes alip 49 which engages a flat counterbored surface (not shown) on thebottom surface of the cover to ensure that the heat sink will contactthe surface of the BGA package. A slot 36 formed in the heat sinkfacilitates threading the heat sink within the cover, for example, witha screwdriver or coin. Other latching mechanisms (e.g., clips orcatches) may also be used to secure BGA packages within the socketconverter assembly. It is also appreciated that other heat sinkarrangements, including those with increased surface area (e.g. heatsinks with finned arrangements), may be substituted for the lowerprofile version shown in FIG. 1. In some applications, a heat sink maynot be required with only the cover providing the downward compressingforce to the BGA package.

Referring to FIG. 2, each converter socket terminal 18 includes a femalesocket 40 positioned within one of the array of holes 20 of insulativemember 16. Female socket 40 includes a solder ball 42 pre-attached(e.g., by soldering) to its bottom end 44 to provide an identical matingcondition to surface mount pads 24 as would have been the case had BGApackage 12 been connected directly to the printed circuit board 14.Solder balls 42 are eventually soldered to corresponding surface mountpads 24 of circuit board 14. Positioned within the interior of femalesocket 40 is a contact spring 46 press-fit within the interior and upperend of the female socket.

Referring to FIG. 3, each contact spring 46 includes spring leaves 48attached at circumferentially spaced points of the lower end of a barrel50. Contact spring 46 is sized to receive a male terminal 52 whichpasses through barrel 50 to frictionally engage spring leaves 48.Contact springs of this type are commercially available from AdvancedInterconnections, West Warwick, R.I. or other stamping outfits providingsuch contact springs (e.g., in an open-tooling arrangement). Springleaves 48 provide a “wiping”, reliable electrical contact to the maleterminal pins by applying a frictional force in a directionsubstantially transverse to the longitudinal axis of the male terminalssufficient to retain the pin within the socket body.

Each male terminal 52 has a head 54 adapted to receive a correspondingball 22 of the BGA package 12 and a pin 56, thereby forming anelectrical connection between ball 22 (FIG. 5B) of package 12 and solderball 42 of converter socket terminal 18. Head 54 has a concave uppersurface 55 for accommodating the rounded shape of solder ball 22.

Referring again to FIG. 2 and FIG. 4, a relatively sharp projection 57may be disposed concentrically on concave upper surface 55 of head 54.Projection 57 is used to pierce the outer surface of the BGA package'ssolder balls 22 which, due to exposure to the atmosphere, may have alayer of oxidation. Projection 57 is positioned at the lowest pointwithin concave upper surface 55 with the tip of projection 57substantially below the plane defined by the outer peripheral edge 67 ofhead 54. Thus, projection 57 is protected during tumbling operations,commonly performed on machined parts to remove sharp and irregularedges.

Referring to FIG. 4A, in an alternative embodiment, contacting surfacesof head 54 a include particle interconnection (PI) 53 contacts. Asdescribed in U.S. Pat. No. 5,083,697 (incorporated by reference),particle interconnection contacts 53 include relatively hard metallizedparticles deposited in a soft metal layer such that they protrude fromthe surface of the contact. When a second contacting surface (e.g.,ball) is compressively brought into contact with the PI contact, thehard particles penetrate any oxides and contamination present on thecontacting surface. PI contacts minimize the resistance between thecontacts, particularly after repeated insertions. Alternatively, adendritic growth process may be used to improve the conductivity betweencontacts.

Referring again to FIG. 2, head 54 of each male terminal 52 alsoincludes a V-groove 59 used to capture a relatively thin polymeric sheet61 made, for example from Kapton® (a product of E.I. DuPont de Nemoursand Co., Wilmington, Del.). Sheet 61 (not shown in FIG. 1 for purposesof clarity) includes openings 63 sized slightly smaller than thediameter of the heads 54. This arrangement maintains male terminals 52together in proper spaced relationship so that the pins can be easilyaligned over and inserted into female sockets 40. Sheet 61 also preventstilting of the pins which can cause electrical shorting.

Each of pins 56 are received within corresponding contact springs 46with spring leaves 48 configured to provide a lateral force, generallytransverse to the longitudinal axis of pins 56, thereby frictionallyengaging outer surfaces of the pins.

In one embodiment, the lower end of pin 56 includes a flattened head 58having has a diameter slightly larger than the diameter of pin 56 sothat after head 58 passes through spring leaves 48 of contact spring 46,male terminal 52 is captured within female socket 40.

Metallic coiled springs 60 are loosely positioned within the interiorsof each of female sockets 40 and provide an upward force to the lowerends of pins 56. As mentioned earlier, spring leaves 48 of contactsprings 46 provide a sufficient amount of lateral frictional forcegenerally transverse to the longitudinal axis of the pins, to ensure areliable electrical contact to pins 56 of male terminals 52. However,when hold-down cover 30 is removed from insulative member 16, guide box26 and BGA package 12, metallic coiled springs 60 expand causing each ofmale terminals 52 to release and extend to their most vertical positionwithin female sockets 40. Thus, it is important that coiled springs 60provide an upward force to male terminal pins 52 that overcomes thefrictional force, transverse to the upward force, applied by springleaves 48. The upward force of coiled springs 60 also minimizes the riskof pins 56 “sticking” within corresponding female sockets 40.

FIGS. 5A and 5B illustrate the operation of converter socket terminals18. Referring to FIG. 5A, BGA package 12 is positioned within guide box26, using sidewalls 28 of guide box 26, and over insulative member 16with solder balls 22 of BGA package 12 resting on concave upper surface55 of male terminals 52. In this position, male terminals 52 verticallyextend from contact springs 46 to their greatest degree.

Referring to FIG. 5B, with cover 30 in use and heat sink 32 are slidover insulative member 16, guide box 26 and BGA package 12. Heat sink 32is rotated within cover 30 using slot 36 until the heat sink contactsthe upper surface of BGA package 12. Further rotation of heat sink 32causes male terminal pins 52 to extend within female sockets 40 andagainst the bias of spring coils 60. Thus, electrical interconnectionsare completed from each of solder balls 22 of BGA package 12 tocorresponding pads 24 of board 14, after solder balls 42 have beensoldered to pads 24. Raising heat sink 32 from cover 30 removes thedownward force applied to BGA package 12 with spring coils 60 returningmale terminal pins 52 to their fully extended vertical position of FIG.5A. With heat sink 32 in its raised position, cover 30 can be removed toallow, for example, substituting a different BGA package within the BGAconverter socket assembly. The likelihood that one or more of maleterminal pins 52 becoming stuck within female socket 40 is minimizedbecause the pins are “ganged” together by polymeric sheet 61 whichassists in ensuring that all of the pins return to their verticallyextended position and at a consistent height. It is also important tonote that each time a BGA package is secured within BGA socket converterassembly 10, pins 56 of male terminals 52 are “wiped” against springleaves 48 of contact spring 46 to remove oxidation and ensure a reliableelectrical connection therebetween.

Other embodiments are within the following claims. For example, incertain applications a reduced spacing or pitch between adjacent solderballs 22 may be required (e.g., 1 mm pitch or less). Referring to FIGS.6 and 7, in such applications, a converter socket assembly 70 includesthe male terminal pin 52 and coiled spring 60 used above in conjunctionwith the embodiment of FIGS. 1-5A and 5B. However, unlike the abovedescribed embodiment, converter socket assembly 70 does not include afemale socket. Rather, converter socket assembly 70 includes a contactspring 72 having spring leaves 74, as well as a leg member 76 extendingto a contact surface 78 having a solder ball 80 pre-attached thereto.Solder resist 75 is applied to a small area near the distal end of legmember 76 to facilitate attachment of solder ball 80 (FIG. 6) to contactsurface 78. Solder resist 75 prevents, during soldering of the solderball to contact surface 78, the solder from wicking up leg member 76.Contact spring is press-fit directly within a hole 82 formed within aninsulative support member 84.

Referring to FIG. 8, in another embodiment of a BGA socket converterassembly 90, the positions of the contact spring and coiled spring arereversed. BGA socket converter assembly 90 includes an electricallyinsulative member 92 having an array of holes 94 extending therethroughin a pattern corresponding to a footprint of rounded solder balls 22 ofBGA package 12 as well as a footprint of surface mount pads 24 ofprinted circuit board 14. Insulative member 92 includes integrallyformed guide members 96 for facilitating insertion of BGA package 12.Insulative member 92, in essence, is an integrally-formed combination ofthe insulative member 16 and guide box 26 of FIGS. 1 and 2. Insulativemember 92 is surrounded by a hold-down cover 98/heat sink 100arrangement, similar to that described above in conjunction with FIG. 1.Positioned within a lower region of each hole 94 is a contact spring 102having a head region 104 with a solder ball 106 attached thereto.Contact spring 102 includes spring leaves 108 which extend vertically toreceive pin 56 of male terminal 52. A coiled spring 110 is positioned inthe upper region of each hole 94 between a detent 112, formed withinhole 94, and head 54 of male terminal 52.

In this embodiment, a retaining sheet 114 supports male terminals 52 andis sized slightly larger in one dimension (e.g., the width) so that oneor more edges (or tabs) 115 of sheet 114 extends into openings 116formed in the guide members 96 of insulative member 92. During assembly,the flexibility of the material permits the edge 115 to be bentsufficiently allowing it to slip within opening. Once in place, edges115 of the sheet help to retain male terminals 52 within convertersocket 90, particularly during handling and soldering of the convertersocket to the printed circuit board.

Other contact spring arrangements may be substituted for the contactspring 102 of BGA socket converter assembly 90. For example, referringto FIGS. 9 and 9A, a miniature contact assembly 150 is positioned withina hole 152 of an insulative support member 154. Miniature contactassembly 150 includes a body 156 having an upper barrel section 157 fromwhich flexing spring fingers 158 extend. Flexing spring fingers receivepins 56 of male terminals 52. Upper barrel section also includesnon-flexing fingers 159 which extend and connect to a lower barrelsection 160 having a reduced diameter end 161 sized to be press-fitwithin a ferrule 162. Ferrule 162, in turn, is press-fit within thelower portion of hole 152 and provides a contact surface 164 where asolder ball 166 is attached. Miniature contact assembly 150 iscommercially available from Ditron Inc., Stormville, N.Y. (Product No.D-14). A coiled spring 168 is positioned in the upper region of hole 152between the upper end of contact assembly 150 and the head 54 of maleterminal 52. In certain applications, ferrule 162 may not be required sothat solder ball 166 directly contacts the distal ends of spring fingers158.

In some applications, it may be desirable to replace male terminals 52.For example, in certain test applications, BGA packages are repeatedlyremoved and inserted in BGA socket converter assembly 90. In theseapplications, the head portion of the male terminal becomes contaminatedwith lead/tin solder from balls 22 of the BGA package or other residue.Build-up of the solder or residue can lead to poor electrical contact tothe head portion.

Referring to FIG. 10, to address this problem, each male terminal pin120 includes spring fingers 122 press-fit within an opening 124 of themale terminal pin. A separate replaceable terminal 126 includes a head128 having a pin 130 received by spring fingers 122. Head 128 includes aV-groove 132 for supporting a flexible retaining sheet 134 used to holdreplaceable terminals 126 in the same manner described above inconjunction with FIG. 2. In the event that heads 128 become clogged withsolder or otherwise contaminated with residue, retaining sheet 134 withreplaceable terminals 126 is removed and discarded and a new retainingsheet with new replaceable terminals 126 is positioned within maleterminal pins 120.

It is also appreciated that in the above described embodiments, otherforms of spring members may be substituted for coiled springs 60 (FIG.2). Referring to FIG. 11, for example, spring-like members 140 formed ofelastomeric (e.g., rubber) or shape-memory materials may be used toprovide the necessary upward force needed to overcome the frictionalforces of contact springs 46.

Still further embodiments are supported by the following claims.

What is claimed is:
 1. A socket terminal assembly of the type configuredto electrically connect an electrical contacting area of an integratedcircuit package to a corresponding connection region of a substrate, thesocket terminal assembly comprising: a socket body having an endconfigured to contact the corresponding connection region of thesubstrate and an opposite end with an opening; a pin having a first endadapted to be received within the opening of the socket body and asecond end to contact the electrical contacting are of the integratedcircuit; a contact spring, disposed at the opening of the socket body,to receive and apply a frictional force sufficient to retain the pinwithin the opening of the socket body; and a resilient member, disposedwithin the opening of the socket body, to apply, in response to adownward force applied to the pin, an upward force to the pin sufficientto overcome the frictional force applied by the contact spring.